Gary,
Obmi has to be my favorite NPC ever. In the 80's, he drove the PC's bonkers (<-- it was the 80's!). When we resumed gaming c. 2000, I brought him out in an old castle/dungeon of my making and once again was my favorite weapon at my DM disposal.
In this dungeon, he was working at a bench when he was approached, feigning to be slaving away. Strangely, nearby was a sliding glass door which looked out to a forest. He stabbed the fighter as they were talking and fled out the glass door. The party of four pursued him, not knowing they were running into "The Repeating Forest", which would repeat itself every 200'. Thus he doubled back on them using its repeating feature and escaped via the sliding door.
My wife will still mention him from time to time whenever we discuss gaming. Bravo on such a great character that really knows how to get under the PCs' collective skin.